The performance of steel cord (brass plated)-rubber composites (e.g., tires) is determined by the properties of the individual components (i.e., steel cord and rubber) as well as by the adhesion between the components. Improvements in aged properties of the steel cord skim compounds and in cord-rubber humid aged adhesion retention are being sought continually in efforts to improve the service life of steel reinforced tires. Unfortunately, some of the compounding variations that can improve cord-rubber adhesion retention (e.g., high sulfur levels, high sulfur/accelerator ratio) have a detrimental effect on aged properties of the rubber compounds. Additives that can improve aged adhesion retention without effecting aged properties of the rubber compound can, therefore, be very valuable in improving the long-term durability of tires.
It has been suggested.sup.1 that "dezincification" of the brass layer during humid aging can be a major cause of loss of brass-rubber adhesion on humid aging. The term dezincification is poorly defined and constitutes a complex set of reactions/processes.sup.1. Corrosion inhibitors for dezincification resistance improvement have, however, not yet been described (page 453).sup.1. A recent brass corrosion study.sup.2 suggests that certain materials such as alizarin (1,2-dihydroxyanthraquinone) may reduce the dezincification of brass sheet (63% Cu and 37% Zn) immersed in 1% H.sub.2 SO.sub.4 solution at 30.degree. C. for two days.
Accordingly, it is an object of the present invention to overcome the difficulties alluded to above and to provide a brass-rubber composite exhibiting an improved brass-rubber bond.
Another object is to increase the resistance of the rubber-brass bond to degradation caused by heat and moisture.
These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description and working examples.